1. Field of the Invention
The present invention relates to rehabilitation devices, and in particular, to an apparatus for imparting continuous passive motion to a lower limb of the human anatomy.
2. Description of the Prior Art
The prior art is replete with examples of devices for passively mobilizing the joint of a person's limbs U.S. Pat. No. 4,549,534, issued to Zagorski et al on Oct. 29, 1985, describes the background and benefits of such devices. Other examples of such apparatuses are described in U.S. Pat. Nos. 4,492,222, Hajianpour, Jan. 8, 1985; 4,509,509, Bouvet et al, Apr. 9, 1985; 4,558,692, Greiner, Dec. 17, 1985; and 4,665,899, Farris et al, May 19, 1987. All of these patents, which represent the prior art, have in common a structure which includes a base, a thigh support first member hinged to the base at one end, and a lower leg support second member hinged to the first member at the other end thereof. A motor means is generally connected to the other end of the second member and the base such that the first and second members can be folded upwardly and extended horizontally relative to the base. In normal use, a patient is in a reclined position with a hip joint adjacent the hinge between the base and the thigh support first member. The patient's respective leg extends over the first and second support members. As the motor is driven, the first and second members fold upwardly and then extend longitudinally, thus passively exercising the supported leg. The cycle is then repeated.
Since the motor is operatively engaged to the other end of the second member, the first and second members fold and extend as a result of a reciprocating push-pull action applied at the other end of the second member. The motor speed can usually be varied, but once set for a given cycle, the speed is generally constant. However, the hinge between the first and second members will be in a continual acceleration-deceleration cycle, depending on the angle between the members, as a result of the constant speed of the motor at one end of the linkage. Since the patient's knee is being flexed at this hinge location, it will be subjected to these fluctuations in speed.